Glazing compositions and process



United States Patent 6 3,532,524 GLAZING COMPOSITIONS AND PROCESSRichard W. Petticrew, Perrysburg, Ohio, assignor to Owens-Illinois,Inc., a corporation of Ohio N Drawing. Filed Oct. 6, 1966, Ser. No.584,661

Int. Cl. C03c /02 U.S. Cl. 106-48 7 Claims ABSTRACT OF THE DISCLOSUREThis invention relates to glazing compositions and to a process ofproduction. More specifically, this invention relates to glazes for verylow-expansion bodies such as glass-ceramic bodies.

GLASS CERAMIC MATERIALS Ceramic materials from thermally crystallizableglasses have become known in the relatively recent art, and manypractical uses have been found for them. Further, due to the veryfavorable properties of low coefficient of thermal expansion, highflexural strength, zero porosity, etc., they have many potential uses asyet untapped. These new ceramic materials can be made by in situcrystallization of a multitude of very small crystals in thermallycrystallizable glasses. The glass composition is provided with anucleating agent to initiate crystal formation. In a usual operation, anarticle is formed of the glass and thereafter crystallization iseffected by programmed heat treatment.

One important glass series that is very well suited to the production ofceramics by the in situ crystallization process is described incopending application Ser. No. 352,958, filed Mar. 18, 1964, now patent3,380,818 assigned to the same assignee as the present invention. Theseglass compositions are capable of producing crystalline ceramics havingan average coefiicient of lineal thermal expansion over the range from0-3 00 C. of less than 25 C.

As distinguished from many of the glasses previously proposed forceramic formation, the reference glasses have good working properties,suitable for commercial melting and automatic machine formingoperations, as well as for lamp working in the glassy state. Thus, theease of working substantially extends the potential of glass ceramics.

The glasses of the above-identified application have liquidustemperatures below 2460 F. and contain at least the following essentialcomponents in the following weight percentage limits, based on the totalcomposition:

TABLE I Oxide: Percent by weight SiO 66-73 A1 0 -19 Li O 2.5-4 MgO 3-7.7ZrO 1-1.7

Ti0 1-1ess than 1.9

, 3,532,524 Patented Oct. 6, 1970 In addition, other useful andpurposely added components include SnO up to 1.7%, P 0 up to 3% (usually0-2), BaO up to 5%, and ZnO up to 3%, all in weight percent of the glasscomposition. Further, small amounts of residual arsenic and antimonyoxides are often present in the compositions, since arsenic and antimonycompounds are often used as fining agents. In actual practice, arsenic,expressed as As O is usually present in amounts not more than 0.3 weightpercent, and antimony, expressed as Sb O is seldom present in amountsover 1 weight percent. Also, Na O, while not particularly desirable, isoften present to a certain degree as an impurity, usually in amounts notover 1.5 Weight percent. Further, when AS203 is used as a fining agent,it is commonly added together with a little NaNO a well-known practice.Another additive sometimes employed is F, usually in amounts notexceeding 0.4 weight percent. It is, of course, added as a salt in theusual manner, and seems to aid the crystallization process somewhat whenit is employed. In summary, then, the compositions contain thefollowing, aside from F and such fining agents as may be used:

Accordingly, the glass and crystalline ceramic compositions of the abovereferenced application have the components of Table II in the amountsnamed as essential ingredients, and the compositions of the inventionalmost always, and certainly preferably, contain from to weight percentof such components, the other 5 to 0 percent being other compatibleinorganic ingredients, usually oxides or halides. Thus, the essentialproperties of the thermally crystallizable glasses are usually lost witha total of over 5 percent of additives not set forth in Table II;indeed, the essential properties can be lost with the addition of 5% orless of such unnamed components, if the attempt be deliberately made.For instance, inclusion of 4 or 5 weight percent of V 0 in glasses ofTable II would produce a glass having a liquidus well above 2460 F.,contrary to an essential feature of the subject glasses.

Accordingly, the invention of the above-identified application providesa substantial step forward in the art by the development ofcrystallizable glass compositions having good melting andformingproperties as glass, and at the same time having good properties as verylow expansion crystalline ceramics after heat treatment. These newcompositions accomplish very difiiculty achieved objectives. Thus, theglass compositions can be crystallized to ceramics having a very fine,homogeneous structure, zero porosity, low coeflicients of thermalexpansion, and generally high fl-exural strengths. All of this isaccomplished by using low amounts of titania and zirconia incombination.

3 THE PROBLEMLow expansion In order to successfully market many kinds ofware made from glass ceramics, it is necessary to apply a decorativeglaze. However, there are no known glazes which can be applied to verylow expansion vitreous bodies such as the above disclosed glass ceramicmaterials. Further, the ceramics have zero porosity and there is notooth by which an overglaze can bond to the base article.

Prior known glazing materials which have been tried for use asdecorative glazes for low expansion glass ceramics have encountered thedifiiculty of peeling. Further, prior efiorts have encountered excessivecrazing problems with attempted glazing compositions for very lowexpansion glass ceramics.

ADVANCE PROVIDED BY THE PRESENT INVENTION The present invention providesa further advance to the art in the form of glazing compositions for lowexpansion bodies of the nature discussed above.

Accordingly, it is an important object of the present invention toprovide novel glazing compositions for application to low expansionglass-ceramic bodies.

A further object is to provide a method of producing glazingcompositions for application to low expansion materials such asglass-ceramic bodies.

A further object is to provide a process for glazing low expansionmaterials such as glass-ceramic bodies.

THE INVENTION By the present invention novel glazes have been providedthat will fuse onto low expansion glass-ceramic bodies (expansion ofless than 25 l0 C.) without peeling and with minimum crazing. Thecompositions of the present invention contain at least the followingessential components in the percentages indicated, based on totalcomposition:

4 and Si0 to impart low-expansion characteristics to the glaze. MgO andC210 help to lower the melting point; these are semi-fluxes. TiO C0 0 FeO NiO, Cr O, MnO and Q10 are colorants.

The above represents the broad workable composition range of ingredientsof the glazes of the present invention. Within the preferred range ofoperation, the following weight percentages of oxides, based on totalcomposition, can be employed:

wherein the amount of R 0 is at least about 2%, and preferably about 3%.

The lower amount of Li O (R 0) is preferred in order to minimizecrazing. K 0 is the less desirable R 0 component. The B 0 lowers themelting point and, in general, provides desired thermal expansionproperties.

Table V illustrates several specific compositions made by the presentinvention and falling within the ranges set forth above. i

TABLE V Composition Number wherein the amount of M 0, Na O and B 0 is atleast about 12.5%.

The Li O, Na O and B 0 function as fluxes to make a low-meltingmaterial. Also, Li O combines with A1 0 PRACTICE OF THE INVENTION Thespecific glazes are formed into finely divided or powdered frit glassesin accordance with the following procedure. The ingredients were admixedand fired under oxidizing conditions in a furnace at a meltingtemperature in a range of about 2,000 to about 2,900 F. By so operating,homogeneous, vitreous compositions were produced. These were formed intoa frit in a suitable manner as by running as a stream or layer overwater-cooled metering rolls, and then into a water quench so that thethermal shock caused the glass to break up into granular frit form.Thereafter, for the practice of the invention, the granules were groundto a particle size as desired, usually in the range from about 250 to400 mesh.

The powdered frit was then admixed with a commercial silk-screeningvehicle such as wax and thermoplastic resin for application to thearticle to be decorated. The vehicle burns away during firing as isknown in the art. Reference is made to US. Pat. 3,089, 782 for adisclosure of silk-screening vehicles.

EXAMPLE I In one example of practicing the invention, a thermallycrystallizable glass was made from the following batch materials:

Ingredient: Parts by weight Petalite 374 Flint 63.7 Alcoa A-10 Alumina 320.3

Periclase 4 22.8 Florida zircon 10.6 Titanox 6 9.0 Aluminummetaphosphate 3.8 Lithium fluoride 8 1.37 Arsenic trioxide 1.25 Niter1.25 Water 25.0

4.2% L120, 16,2% A1 03, 77.7% S102, 0.4% Na O, 0.2% K20 and 0.027%FezOs, and other minor impurities, including 1% ignition loss.

B 99.5% A1208, 0.03% F6203, 0.1% Nan-:0, 0.08% S102, 0.2+ ignition loss.

4 95.3%) MgO, 0.5% F6203, 2.8% S102, 0.3% A1203, and 1.1% a

5 66 Z102, 33.35% iSiOz, 0.25% T102, 0.1% F9203.

Substantially pure T102.

" Substantially pure, except about 1% ignition loss.

5 Essentially pure, ME.

The above ingredients produced a theoretical composition as follows:

Oxide: Parts by weight Si -1 71.63 A1 0 16.5 MgO 4.4 Li O 3.3 ZrO 1.4TiO 1.8 Na O 0.2 2

The batch materials were melted at about 2900 F. for about 43 hours in ahigh-alumina refractory tank furnace, using a slight excess of air inthe fuel gas mixture, to provide an oxidizing atmosphere.

During the melting of the glass a good percentage of the AS203 and Fwere removed by volatilization. The analyzed composition of the glasswas as follows:

Oxide: Percent by weight SiO 71.2 A1 0 17 MgO 4.3 Li- O 3.2 ZrO 1.3 Ti0011.8 F P 0 0.6 N21 O 0.5

The glass had an annealing point of approximately 1210 F.; a log 4viscosity temperature of about 2390 F.; and, a liquidus temperature ofabout 25 55 F. A number of glass rods (canes) were pulled from the tankduring the time that the glass was at a temperature in the range fromabout 2425 F. down to 2275 F. The canes were about 7 in diameter. Also,a number of 5 ounce tumblers were made from the glass in a paste mold,and several 5" diameter bowls were pressed from the glass in a pressmold.

The canes and formed articles were subsequently heat treated as follows:

All articles were rather rapidly heated to 1100 F.; thereafter, theheating schedule was as follows:

' 6 11001200 F. at a rate of 145/hr.; 1200-1300 F. at a rate of 25/hr.;1300-1600 F. at a rate of 50/hr.; 1600l950 F. at a rate of 145/hr.;

Held at 1950 F. one hour; and,

Cooled at a rate of about 400 F./hr. to ambient temperature.

The heat treated articles were white, very fine grained, glossy andstrong. Specifically, the modulus of rupture of the abraded rods testedwas 19,000 p.s.i., and they withstood thermal shock when plunged intowater at about 1300 F. temperature differential. Thus, the rods were atabout 1380" F., while the water was at about F. or'

less. The measured average coeflicient of lineal thermal expansion ofthe rods was 18.7 l0 between 26 C. and 694 C.

Formed articles of the above glass-ceramic were glazed with acomposition No. 9 of the present invention. The procedure was asfollows:

A dip coating was made by admixing a powdered frit glass No. 9 with asilk-screening vehicle. This dip coating was applied to 5" diametergreen, uncrystallized, glass bowls. Then, the bowls were heat treatedaccording to the schedule shown above, which was effective tosimultaneously fire the glaze.

EXTENDED SCOPE OF INVENTION The glass-ceramic compositions discussedabove, with reference to copending application Ser. No. 352,958, filedMar. 18, 1964, are exemplary of the use of the present invention.Additionally, the glazes of the present invention are applicable to usewith other low expansion glassceramics known in the art. These aretypified by U.S. Pat. 3,117,881 to Henry et al.; German Pat. 1,099,135;Belgian Pat. 609,529 to Fuji Photo Film Company, Ltd.; Japanese PatentPublication 3912/63 (Apr. 20, 1963); and, French Pat. 1,337,180, datedJuly 29, 1963, to Fuji Photo Film Company.

The glazes of the present invention are fusible at temperatures that arenot harmful to the glass-ceramic ware. The upper level is, therefore,determined by the vitrification of the glass-ceramic ware. An exemplaryglass ceramic provides a fusing limit of about 1900 F.

Further, the glazes of this invention adhere well to the glass-ceramicWare with a minimum of crazing.

Generally, thin coatings are preferred for optimum results.

What is claimed is:

1. A glazing composition for glass-ceramic materials having acoefficient of thermal expansion over the range 0300 C. of less than 25l0-' C., the glazing composition consisting essentially of the followingcomponents:

Oxide: Percent by weight Si0 73.97 A1 0 9.59 Li O 14.41 C0304 2. Aglazing composition for glass-ceramic materials having a coefiicient ofthermal expansion over the range 0300 C. of less than 25 X l0''/ C., theglazing composition consisting essentially of the following components:

Oxide: Percent by weight sio 70.0 C0304 MgO 5.0 B 0 24.5

3. A glazing composition for glass-ceramic materials having acoeflicient of thermal expansion over the range 0-300 C. of less than 25l0' C., the glazing composition consisting essentially of the followingcomponents:

Oxide: Percent by weight SiO 70.0 Li O 5.0 C0304 B 24.5

4. A glazing composition for glass-ceramic materials having acoeflicient of thermal expansion over the range 0-300 C. of less than 2510' C., the glazing composition consisting essentially of the followingcomponents:

Oxide: Percent by weight sio 70.0 C0 0 0.5 B 0 24.5 Na O 5.0

5. A glazing composition for glass-ceramic materials having acoefiicient of thermal expansion over the range 0300 C. of less than 25X C., the glazing composition consisting essentially of the followingcomponents:

6. A glazing composition for glass-ceramic materials having acoefiicient of thermal expansion over the range 0300 C. of less than 2510- C., the glazing composition consisting essentially of the followingcomponents:

8 Oxide: Percent by weight SiO 72.0 Li O 3.0 C0304 B 0 24.0

7. A glazing composition for glass-ceramic materials having acoefiicient of thermal expansion over the range 0300 C. of less than 2510-' C., the glazing composition consisting essentially of the followingcomponents:

Oxide: Percent by Weight SiO 70.0 C0304 1.0 B 0 24.0 N320 ReferencesCited UNITED STATES PATENTS 2,239,551 4/1941 Dalton et a1 10654 XR2,741,008 4/1956 Snoddy 117--125 XR 2,971,853 2/1961 Stookey 10654 XR3,019,116 1/1962 Goucette 10648 XR 3,051,592 8/1962 Woerner 10654 XR3,200,310 8/1965 Carman 106-54 XR 3,226,342 12/ 1965 Kesten 10654 XR3,349,275 10/1967 Blum et al. 10654 XR 3,368,712 2/1968 Sanford et a110648 XR 3,384,508 5/1968 Bopp et a1. 10639 FOREIGN PATENTS 1,287,584 6/1963 France.

(2nd addition to No. 80,991)

HELEN M. MCCARTHY, Primary Examiner US. Cl. X.R.

